Plunger Fuel Pump for an Internal Combustion Engine

ABSTRACT

A plunger fuel pump for an internal combustion engine includes a pump cylinder and a pump plunger that is axially displaceable in the pump cylinder. The plunger fuel pump has a seal with an annular basic structure arranged around the circumference of the pump plunger. The seal is produced by injection molding in an axial injection direction.

PRIOR ART

The invention relates to a piston fuel pump in accordance with thepreamble of claim 1.

Fuel systems of internal combustion engines are known from themarketplace, in which fuel systems the fuel is delivered from a fueltank under high pressure by means of a mechanically driven piston fuelpump into a fuel rail and passes from there via injectors intocombustion chambers of an internal combustion engine.

In the piston fuel pump which is known from DE 10 2004 063 074 A1, forexample, a displaceably mounted pump piston is provided which compressesfuel in a delivery space of the piston fuel pump. The pump piston isguided in a piston bushing with a small sealing gap and such that itslides by way of a close fit. In order to support and seal via a gapseal, the piston bushing has to have a certain length and possiblyabsorb great transverse forces. Therefore, the piston bushing is oftenproduced from steel. On account of high tolerance requirements,moreover, what is known as a “piston pairing” is used, that is to sayeach pump housing is assigned a defined piston. Furthermore, thecylinder in the pump housing has to be honed in a complicated manner.There is a requirement for a fuel piston pump which is less complicatedto produce.

DISCLOSURE OF THE INVENTION

The problem on which the present invention is based is solved by way ofa fuel piston pump having the features of claim 1. Advantageousdevelopments of the invention are mentioned in the subclaims. Moreover,further features which are important for the invention are found in thefollowing description and in the drawing.

The piston fuel pump according to the invention has the advantage that apiston bushing and the corresponding highly accurate fit of the pistonin the piston bushing are no longer absolutely necessary and thereforeconsiderable costs can be saved. Instead, the piston fuel pump has aseal which is arranged on the circumference of the pump piston.

According to the invention, said seal has an annular basic structure, inparticular it runs once around the pump piston in the circumferentialdirection. To this extent, reference can also be made in the followingtext to an axis of the piston, that is to say an axial direction, inorder to identify an excellent direction of the seal.

The fuel piston pump is, in particular, a pump which has a pump housing,in which a working space which is delimited by the pump piston isformed. The compression of the fuel takes place, in particular, in saidworking space, in particular by way of an axial movement of the pumppiston which reduces the size of the working space. In particular, acompression of the fuel in the working space takes place to a highpressure level, for example to from 100 bar to 600 bar.

The seal according to the invention is configured, in particular,between the working space and a low pressure region of the pump. Thepressure in the low pressure region is lower than the high pressurelevel which is generated in the working space of the pump. The pressurelevel in the low pressure region can lie, for example, at from 3 bar to10 bar and can be generated by way of a separate forepump.

The working space is connected, in particular, via an outlet valve to apump outlet and is connected, in particular, via an electricallyactuable inlet valve to a pump inlet. The electrically actuable inletvalve can be configured, in particular, as a quantity control valve. Asan option, furthermore, a damping device for damping pulses in the lowpressure region of the pump can additionally be provided between thepump inlet and the working space.

The damping device for damping pulses in the low pressure region cancomprise, for example, a gas volume which is enclosed between twodiaphragms: details with regard to the damping device can be configuredas shown in DE10327408A1.

A further valve which is arranged between the pump outlet and theworking space and is arranged in an antiparallel manner with respect tothe outlet valve can be provided and can act, in particular, as apressure limiting valve for a high pressure accumulator which can beconnected to the pump.

The outlet valve and/or the inlet valve and/or the pressure limitingvalve are/is preferably fixed in a stationary manner with respect to thepump housing and to this extent also in a stationary manner with respectto the pump cylinder. Fixing of said components on the pump piston isruled out in this regard, in particular. The advantage arises that themass of the pump piston is low and therefore the dynamics and/or ease ofmovement of the pump is/are improved.

In addition or as an alternative, the pump piston is preferablyconfigured as a solid body, with the result that it can withstand thehigh pressures which act during the fuel injection, in particular in thecase of direct gasoline injection, without deformation. A capability offlow to pass through the pump piston in the longitudinal direction isruled out in this regard.

Further details of the arrangement of the working space, outlet valveand pressure regulating valve with respect to one another and in thepump body can be configured, for example, as shown in DE102004013307A1.

The pump cylinder can be configured in a bushing which is fixed in thepump body. As an alternative, the pump cylinder can also be provideddirectly in the pump body.

The pump body, the pump piston, the pump cylinder and/or all pump partswhich come into contact with the fuel preferably consist only of steelsand of plastics, such that there is a high resistance even toethanol-containing fuels and/or other aggressive fuels as a result.

According to the invention, the seal is manufactured by means ofinjection molding. The injection molding process which is also calledinjection molding is known in principle to a person skilled in the art,in particular for manufacturing workpieces from plastic, such as fromthermoplastics.

One special feature of said method consists, in particular, in that aliquefied injection molding compound is introduced into an injectionmold through an injection opening or through a plurality of injectionopenings. Here, the air which is initially present in the injection moldescapes, in particular, via a separate venting opening or via aplurality of separate venting openings. After cooling, the manufacturedworkpiece solidifies and can be removed from the injection mold. Inparticular, the workpiece which is manufactured in this way hasdeviations from the desired shape in the region which lay adjacentlywith respect to an injection opening or a venting opening in theinjection mold. To this extent, in particular, injection points andventing points can be found on workpieces, which are also calledinjection nipples and venting nipples. In particular, they have the formof a local, for example annular, unevenness or an annular burr; elevatedgeometries which can be shaped like small warts can also occur overall.Small recesses can also occur, in particular, in the region of theventing points.

The invention is based on the observation that, in the case of seals forpiston fuel pumps, injection and venting points of this type either haveto be removed in a complicated manner by way of reworking or can bedisadvantageous for the sealing function and/or for the capability ofthe seal to be mounted and/or handled.

According to the invention, said problem is solved by virtue of the factthat the seal is produced by means of injection molding with an axialinjection direction.

Here, in particular, at least one injection point comes to lie on anaxially oriented surface of the seal and therefore outside the sealingregion of the seal. Developments of the invention can provide that aplurality of injection points are arranged on an axially orientedsurface of the seal.

In developments, a venting point or a plurality of venting points can bearranged on an axially oriented surface of the seal. It is preferredhere that the venting point or the venting points is/are arranged on anaxially oriented surface of the seal which lies opposite that axialsurface in the axial direction, on which the injection point lies or onwhich the injection points lie.

With the same effects and advantages as those mentioned above, inaddition or as an alternative at least one injection point and at leastone venting point can be arranged offset with respect to one another inthe axial direction.

In particular, in the case of the use of the piston fuel pump in thearea of gasoline direct injection, the seal is exposed to highmechanical loads. Therefore, seals made from thermoplastics which arefiber-reinforced are preferred. Fibers made from glass and/or carbon arepreferred. Fiber-reinforced thermoplastic materials with mean fiberlengths of at least 100 μm are preferred. It is preferred in addition oras an alternative that the fiber proportion lies in the range from 5% byweight to 30% by weight. The use of fiber-reinforced PEEK orfiber-reinforced PA is preferred, for example PEEK 150CA30 or PA66CF20.

Fiber-reinforced thermoplastic materials as a rule have anisotropicmaterial properties depending on the fiber orientation, such asanisotropic elasticity. The seal of the piston fuel pump according tothe invention is loaded greatly both in the axial and in the radialdirection, however; to this extent, anisotropic material properties ofthe seal are undesired.

In the present case, anisotropic material properties of the seal in thecase of the use of fiber-reinforced thermoplastic materials can beavoided by virtue of the fact that an ordered orientation of the fibersis avoided.

To this extent, a further independent invention consists in a pistonfuel pump for an internal combustion engine having a pump cylinder and apump piston which can be displaced axially in the pump cylinder, whichpiston fuel pump is distinguished by the fact that the piston fuel pumphas a seal which is arranged on the circumference of the pump pistonwith an annular basic structure made from a fiber-reinforcedthermoplastic material, in which the orientation of the fibers isunordered. Developments within the context of the features which aredisclosed in the present case, in particular in the claims, thedescription and the drawing, are always possible.

An unordered or non-ordered orientation of the fibers in afiber-reinforced thermoplastic material is understood to mean that thereis not a significant preferential direction of the fiber orientationeither globally or locally within the seal. The fiber orientation can bepresent, in particular, in a chaotically unordered manner.

In contrast, it is also known that, in the case of injection molding offiber-reinforced thermoplastic materials, there is the tendency that thefibers are oriented with respect to one another locally or evenglobally, in accordance with the interactions of the fibers among oneanother and with the injection mold which occur during the flow. Theavoidance of an orientation of this type is therefore a challenge, inparticular, in the case of long fibers (mean length greater than 100μm).

In the present case, it can be provided for this purpose that the atleast one injection point and the at least one venting point arearranged offset with respect to one another in the circumferentialdirection. Pronounced thorough mixing and swirling of the liquefiedinjection molding material therefore occurs in the injection mold.

As an alternative or in addition, it can be provided for this purposethat a plurality of injection points are provided on an axial side ofthe seal, and that at least one venting point is provided on theopposite axial side of the seal between the injection points in thecircumferential direction. In this way, even more improved thoroughmixing of the liquefied injection molding material occurs in theinjection mold.

As an alternative or in addition, it can be provided for this purposethat a plurality of venting points are provided on the opposite axialside of the seal, and that the venting points are always arranged offsetin the circumferential direction with respect to the injection points,in particular centrally in the circumferential direction. In this way,thorough mixing of the liquefied injection molding material which isonce again improved occurs in the injection mold.

In the following text, examples of the present invention will beexplained in greater detail with reference to the appended drawings, inwhich:

FIG. 1 shows a diagrammatic illustration of a fuel system of an internalcombustion engine with a detail of a piston fuel pump according to theinvention,

FIG. 2 shows an enlarged sectional illustration of the detail of thepiston fuel pump according to FIG. 1,

FIG. 3 shows an alternative embodiment of the piston fuel pump,

FIG. 4 shows a further alternative embodiment of the piston fuel pump,

FIGS. 5 and 6 show the seal axially from above and below, and

FIG. 7 shows an axial end region of the seal on an enlarged scale.

EMBODIMENTS

In FIG. 1, a fuel system of an internal combustion engine is given thedesignation 10 overall. It comprises a fuel container 12, from which anelectric forepump 14 delivers the fuel into a low pressure line 16. Thelatter leads to a high pressure pump in the form of a piston fuel pump18. From the latter, a high pressure line 20 leads to a fuel rail 22. Aplurality of injectors 24 which inject the fuel directly into combustionchambers (not shown) which are assigned in each case to them areconnected to said fuel rail 22.

The piston fuel pump 18 comprises a pump housing 26 which is indicatedonly in regions and in which a pump piston 28 is guided or mounteddisplaceably. Said pump piston 28 can be set into a to and fro movementby a cam drive (not shown), which is indicated by way of a laterallyillustrated double arrow 30. The pump piston 28 is loaded by a helicalspring 32 into a bottom dead center in FIG. 1. The pump piston 28 andthe pump housing 26 delimit a delivery space 34. Said delivery space 34can be connected via an inlet valve 36 to the low pressure line 16.Furthermore, the delivery space 34 can be connected via an outlet valve38 to the high pressure line 20.

Both the inlet valve 36 and the outlet valve 38 are configured as checkvalves. Here, an embodiment of the inlet valve 36 as a quantity controlvalve is not shown but is possible. In an embodiment of this type, theinlet valve 36 can be normally open during a delivery stroke of the pumppiston 28, with the result that the fuel is delivered not into the fuelrail 22, but rather back into the low pressure line 16. As a result, thefuel quantity which is delivered into the fuel rail 22 by the pistonfuel pump 18 can be set.

The pump piston 28 is guided in a pump cylinder 40 which to this extentis part of the pump housing 26. At an end which faces the delivery space34, the pump piston 28 has an upper end section 42 in FIG. 1. In thevicinity of said upper end section 42, furthermore, the pump piston 28has a circularly annular step 44 in the manner of a radially projectingcircumferential collar. A seal 46 comes into contact with the pumppiston 28 or with the step 44.

At its end which faces away from the delivery space 34, furthermore, thepump piston 28 has a lower end section 52 in FIG. 1. In the vicinity ofsaid lower end section 52, a guide sleeve 54 is arranged fixedly on thepump housing 26. An 0-ring seal 56 is provided in a groove 58 betweenthe guide sleeve 54 and the pump housing 26. The guide sleeve 54 has acylindrical section 60 which extends coaxially with respect to the pumppiston 28 and by way of which the helical spring 32 is guided. Along apiston longitudinal axis 62, the helical spring 32 dips at least insections into a spring receiving groove 64 of the guide sleeve 54, whereit is supported axially against the guide sleeve 54.

Furthermore, the guide sleeve 54 has a circularly cylindrical receivingsection 66 in the interior, which receiving section 66 is formedsubstantially by way of the inner circumferential wall of thecylindrical section 60. An annular sealing element 68 is arranged in astationary manner relative to the pump housing 26 in said receivingsection 66, the sealing element 68 having an H-shaped cross section.Furthermore, a guide element 72 is likewise arranged in a stationarymanner relative to the pump housing 26 in a collar section 70 whichextends radially inward at the projecting end of the cylindricalsection. Together with the seal 46, said guide element 72 which istherefore spaced apart clearly from the seal 46 as viewed in the axialdirection of the pump piston 28 provides the guidance or two-pointmounting of the pump piston 28.

The configuration of the region of the seal 46 and its mounting is ofparticular importance in the present case.

Said aspects will therefore be described in detail with reference to thefollowing FIGS. 2-7.

FIG. 2 shows the region of the seal 46 of the piston fuel pump 18. In alower region in FIG. 2, the seal 46 is pushed over the step 44 of thepump piston 28 to such an extent that it comes into axial contact withthe step on a shoulder 469 which is configured on it. In particular,that material region of the seal 46 which is present radially outsidethe outer circumferential face of the step 44 forms a bearing or guideregion 48, by way of which the pump piston 28 is guided in a slidingmanner in the pump cylinder 40 and is mounted radially.

From an inner circumferential wall of the pump cylinder 40, the guideregion 48 has a spacing of approximately 2/100 mm which cannot be seenin the figures. In the axial direction, that is to say along the pistonlongitudinal axis 62, the sealing region 50 which is configured as asealing lip 467 extends toward the delivery space 34 in a manner whichadjoins the guide region 48. Here, the sealing lip 467 extendssubstantially coaxially with respect to the pump piston 28 as a tubularsection which is integrally formed on the guide region 48 and isprestressed elastically radially to the outside. The sealing lip 467bears against the inner circumferential wall of the pump cylinder 40. Insaid example, the guide region 48 and the sealing region 50 areconfigured in one piece.

A cap 101 is pushed axially onto the pump piston 28, which cap 101 comesinto contact with the seal 46 radially inward of the sealing lip 467 andon the working space side of the shoulder 469. The cap 101 is seatedfixedly on the pump piston 28 by way of radial pressure and exerts anaxially acting force on the seal 46. The seal 46 which is arrangedbetween the cap 101 and the step 44 of the pump piston 28 is thereforeunder axial prestress.

In said example, the cap 101 is configured as a sleeve 101 a, that is tosay it has the form of a ring or tubular section which is open on twosides. The sleeve 101 a is pushed completely onto the pump piston 28 andterminates flush with the latter on the working space side. As analternative, pushing the sleeve 101 a yet further onto the pump piston28 or a projection on the working space side of the sleeve 101 a wouldlikewise also be possible in principle and possibly practicable.

FIG. 3 shows one alternative to the configuration of the cap 101 as asleeve 101 a. Here, the cap is configured as a cup 101 b. The cup 101 bhas a cup bottom and a cup wall and is pushed onto the pump piston 28with its open end first.

In the example which is shown in FIG. 3, the cup 101 b is pushedcompletely onto the pump piston 28. To this extent, its bottom comesinto contact with the end side of the piston.

In said example, the cup bottom has a small hole 300 in the sectionalplane of FIG. 3, through which small hole 300 air can escape from thecup when the cup 101 b is pushed onto the pump piston 28.

In principle, in particular in the embodiments as a sleeve 101 a or as acup 101 b, the cap 101 can be produced as a deep drawn part, for examplemade from steel. The cap 101 preferably consists of a material, thecoefficient of thermal expansion of which coincides or approximatelycoincides with that of the pump piston 28.

For example, the cap 101 can consist of the same material as the pumppiston 28. Furthermore, the cap 101 can be configured, for example, witha wall thickness of 1 mm.

In the preceding examples, the seal 46 is configured axially between thecap 101 and a step 44 which is configured in one piece on the pumppiston 28. In principle, the one-piece nature is not absolutelynecessary. A simplification in terms of production technology ispossible by virtue of the fact that the step 44 is realized by way of acirclip which is inserted into a groove of the pump piston 28.

FIG. 4 shows yet another solution in this regard. Here, a hat-shapedholding element 102 is pushed with its opening first over the workingspace-side end of the pump piston 28. Here, a bottom 102 a of theholding element 102 comes axially into contact with the end side of thepump piston 28, and a side wall 102 c of the holding element 102 comesinto contact radially with the pump piston 28. A rim 102 b of theholding element 102 which lies axially opposite the bottom 102 a of theholding element 102 is spread radially and to this extent forms a step44.

As in the examples which are shown in FIGS. 2 and 3, the seal 46 is incontact with the step 44 which to this extent is provided in afunctionally identical manner.

In said example, the pump piston 28 has a uniform diameter along itsentire length. Particularly simple and inexpensive production, forexample machining of the pump piston 28 by means of throughfeedgrinding, that is to say with a stationary grinding disk, is possible inthis way.

It is provided in the exemplary embodiments which are shown in FIGS. 2,3 and 4 that the seal 46 has at least one integrally formed bump 461which points in an axial direction, and that the seal 46 bears axiallyvia the at least one bump 461. By way of example, in said examples, theseals 46 even have in each case a plurality of bumps 461 which point inthe direction of the working space 34 and via which the seal 46 bearsagainst the cap 101 and is prestressed axially as a result. In saidexample, the bumps 461 have a hemispherical design. As an alternative,they might also be conical or frustoconical. The bumps 461 have, forexample, a diameter of approximately 0.6 mm, approximately 10% of thediameter of the seal 46, and a height of approximately 0.3 mm,approximately 10% of the height of the seal 46.

Even if the cap 101 bears against the bumps 461 under stress, theresulting deformation of the bumps 461 is so comparatively low thatbearing of the cap 101 against a region of the seal 46 which liesbetween the bumps 461 in the circumferential direction is suppressed.

FIG. 5 shows the seal 46 in plan view, from above in relation to FIGS.2, 3 and 4. It can be seen that a total of eight bumps 461 which areformed integrally on the seal 46 point in the direction of the workingspace 34, which bumps 461 are arranged on an imaginary circular ringabout the piston axis 62 and are spaced apart from one another in thecircumferential direction in each case by 45°.

It goes without saying that the bumps 461 might also be configured inaddition or as an alternative on the axially opposite side of the seal46, on the step 44, in an otherwise unchanged manner.

In said examples, the seal 46 consists of the fiber-reinforcedthermoplastic material PEEK 150CA30 or PA66CF20 and is produced by meansof injection molding. Via the injection molding technique which isexplained in the following text, and in particular the arrangement ofthe injection points 462 and the ventilating points 463, it can beachieved that the orientation of the fibers is disordered.

Here, the injection molding takes place via injection points 462 whichcan be seen in FIG. 5, lie on a common imaginary circular line with thebumps 461 and are spaced apart from one another by 90° in thecircumferential direction. The injection points 462 appear on thefinished product, for example, as small annular or crescent-shaped burrsor as small warts. The injection points have a diameter of 0.9 mm or ofnot more than 0.9 mm.

Furthermore, the injection molding takes place via ventilating points463 which are arranged on the axially opposite side of the seal 46, onthe bottom in FIGS. 2, and 4. They can be seen in FIG. 6. In the presentcase, eight ventilating points 463 are provided which lie on animaginary circular line and are spaced apart from one another by 45° inthe circumferential direction. The ventilating points 463 have adiameter of 0.7 mm or of not more than 0.7 mm and appear on the finishedproduct, for example, as small cavities.

It can be provided that injection points 462 and ventilating points 463are always arranged offset in the circumferential direction with respectto one another. In this way, improved thorough mixing of the liquefiedinjection molding material takes place in the injection mold and adirected orientation of the fibers is avoided and anisotropic materialproperties of the seal 46 are avoided.

In the present case, an axial end region 464 of the seal 46 isconfigured on the sealing lip 467 on the working space side. FIG. 7shows a detail of the seal 46 which is once again enlarged accordingly.

It is provided that a radially outwardly lying surface of the seal 46which lies opposite an inner surface of the pump cylinder 40 is inclinedin an axial end region 464 of the seal 46 radially inward at an angle aof from 10° to 60° with respect to the inner wall of the pump cylinder40. This has the effect, or it is provided as an alternative, that arelative movement between the pump cylinder 40 and the pump piston 28 inthe axial direction, in particular in the direction toward the workingspace 34, aids raising up of the seal 46 from the pump cylinder 28 in aradially inwardly pointing direction. In this case, a liquid film whichconsists of fuel is formed between the seal 46 and the pump cylinder 40,which liquid film considerably reduces the wear of the piston fuel pump18 with a small leakage.

For this purpose, an outwardly pointing, circumferential web 468 isintegrally formed at or on the sealing lip 467, which web 468 hasapproximately the shape of an isosceles triangle in the longitudinaldirection in cross section, of which isosceles triangle the two oppositeacute corners point in axial directions and the third obtuse corner ofwhich bears against the pump cylinder 40 (statically). It is providedthat merely said web comes into contact (statically) with the pumpcylinder 40, whereas the seal 46 or the sealing lip 467 is otherwisespaced apart from the pump cylinder 40 by a gap. A width s of the gapis, for example, 20 μm. In the case of a relative movement, as depictedabove, raising up of the web 468 from the pump cylinder 40 is alsoprovided, furthermore.

1. A piston fuel pump for an internal combustion engine, the piston fuelpump comprising: a pump cylinder; a pump piston configured to bedisplaced axially in the pump cylinder; and a seal having an annularbasic structure, wherein the seal is arranged on a circumference of thepump piston, and wherein the seal is produced by injection molding withan axial injection direction.
 2. The piston fuel pump as claimed inclaim 1, wherein: the seal has at least one injection point and at leastone venting point, and the at least one injection point and the at leastone venting point are arranged offset with respect to one another in anaxial direction.
 3. The piston fuel pump as claimed in claim 2, whereinthe at least one injection point and the at least one venting point arearranged offset with respect to one another in a circumferentialdirection.
 4. The piston fuel pump as claimed in claim 1, wherein: aplurality of injection points are provided on a first axial side of theseal, at least one venting point is provided on a second axial side ofthe seal between injection points of the plurality of injection pointsin a circumferential direction, and the first axial side of the seal isopposite the second axial side of the seal.
 5. The piston fuel pump asclaimed in claim 1, wherein: a plurality of injection points areprovided on a first axial side of the seal, a plurality of ventingpoints are provided on a second axial side of the seal, each ventingpoint of the plurality of venting points is offset in a circumferentialdirection with respect to each injection point of the plurality ofinjection points, and the first axial side of the seal is opposite thesecond axial side of the seal.
 6. The piston fuel pump as claimed inclaim 1, wherein: a plurality of injection points are provided on afirst axial side of the seal, a plurality of venting points are providedon a second axial side of the seal, each venting point of the pluralityof venting points is arranged approximately centrally in acircumferential direction with respect to in each case two adjacentinjection points, and the first axial side of the seal is opposite thesecond axial side of the seal.
 7. The piston fuel pump as claimed inclaim 2, wherein at least one of the at least one injection point andthe at least one venting point is a locally uneven structure.
 8. Thepiston fuel pump as claimed in claim 1, wherein the seal has afiber-reinforced thermoplastic material.
 9. The piston fuel pump asclaimed in claim 8, that wherein fibers in the fiber-reinforcedthermoplastic material are oriented anisotropically.
 10. The piston fuelpump as claimed in claim 8, wherein fibers in the fiber-reinforcedthermoplastic material have a mean length of greater than or equal to100 μm.
 11. The piston fuel pump as claimed in claim 8, wherein fibersin the fiber-reinforced thermoplastic material have carbon.
 12. Thepiston fuel pump as claimed in claim 8, wherein the seal has PEEK. 13.The piston fuel pump as clamed in claim 8, wherein fibers in thefiber-reinforced thermoplastic material consist of carbon.